The use of a semiconductor element across a pair of separating contacts in an electric circuit to eliminate arcing and prevent contact damage is already known. Various circuits have been proposed to turn on the semiconductor prior to contact separation to allow the semiconductor to transfer the circuit current away from the contacts for a sufficient time to allow the contact separation to increase and the contact temperature to decrease to such an extent that arcing is eliminated. Other circuits have been proposed to turn off the semiconductor once the contacts have been separated to prevent the semiconductor element from becoming overheated and damaged by excess circuit current.
U.S. patent application Ser. No. 610,947 filed May 16, 1984 in the name of E.K. Howell describes a voltage dependent element in parallel with a semiconductor element to transfer the circuit current away from the semiconductor. Also disclosed is the arrangement of a capacitor in the base-collector circuit of the semiconductor to turn on the semiconductor and a saturable core current transformer in the base-emitter circuit to turn off the semiconductor and transfer the circuit current to a voltage dependent element. This application is incorporated herein for purposes of reference and should be reviewed for a good description of the relationship between circuit voltage and circuit current during the interruption process.
The use of a capacitor in the base-collector circuit of a bipolar transistor across a pair of contacts to turn on the transistor when the contacts are opened is disclosed within U.S. Pat. No. 4,438,472 in the name of George K. Woodworth. A diode in the base-emitter circuit of the transistor discharges the capacitor when the contacts are closed. It is believed that the use of such a circuit arrangement within residential and industrial power circuits would require too large a capacitor and diode to make such an arrangement commercially feasible.
U.S. Pat. No. 3,601,622 in the name of Sigurd G. Waaben discloses the use of a charge storage diode across a pair of contacts to prevent contact arcing. When the contacts are opened the diode short circuits the contacts to prevent arcing until the charge accumulated in the diode is depleted. The invention is disclosed for use within low power circuits such as an automobile ignition system.
One purpose of the instant invention is to provide an inexpensive and practical means for storing charge in a power transistor connected across a pair of separable contacts so that the transistor turns on when the contacts are separated to transfer current away from the contacts to eliminate arcing. An additional purpose of the invention is to turn off the transistor once the contacts have separated in order to transfer the current to a voltage dependent element thereby interrupting the current without damaging the transistor.